1. Field of the Invention
The present invention relates generally to an information recording and reproducing apparatus, such as a VTR (video tape recorder), and, more particularly, to a pinch roller type tape drive for such an information recording and reproducing apparatus.
2. Description of the Prior Art
FIGS. 6 to 8 show a conventional pinch roller type tape drive incorporated into a VTR. The tape drive comprises a pinch roller 1, and a capstan 8. The pinch roller 1 comprises a pinch roller shaft 4 provided at its opposite ends with flanges 5, a core sleeve 2 rotatably supported at its opposite ends on bearings 3 on the pinch roller shaft 4, and a rubber coat 1a coating the circumference of the core sleeve 2. The working length l.sub.1 of the pinch roller 1 is sufficiently greater than the width l.sub.2 of a magnetic tape 6. A pinch roller pressing member 7 presses the pinch roller 1 at the flanges 5 to apply a pressure T on the order of 4 to 5 kg for a VTR to press the pinch roller 1 elastically against the capstan 8 to pinch the magnetic tape 6 between the pinch roller 1 and the capstan 8 at the pressure T.
When the pinch roller 1 is thus pressed, a depression 1b of a depth substantially corresponding to the thickness t of the magnetic tape 6 is formed in a central portion of the rubber coat 1a in contact with the magnetic tape 6, and the upper and lower end portions 1c of the rubber coat 1a each of a length l.sub.3 =(l.sub.1 -l.sub.2)/2 extending respectively beyond the upper and lower edges 6c of the magnetic tape 6 are pressed against the capstan 8 in relatively large widths of contact area W.sub.1 at the upper edge of the magnetic tape 6 and W.sub.1 ' at the lower edge of the magnetic tape 6. The pinch roller 1 is driven frictionally for rotation by the capstan 8 through the frictional engagement of the upper and lower end portions 1c of the pinch roller 1 and the capstan 8. Consequently, the magnetic tape 6 is driven for running by the combined effect of a frictional driving force applied by the capstan 8 to one surface 6a of the magnetic tape 6 and a frictional driving force applied by the pinch roller 1 to the other surface 6b of the same.
The rubber coat 1a of the pinch roller 1 is inevitably subject to chemical degradation, abrasion and compressive deformation, and hence the depression 1b will grow progressively into a permanent circumferential groove, so that the pressure applied to the magnetic tape 6 by the depression 1b of the pinch roller 1 decreases in the long run below the normal pressure T even if pinch roller 1 is pressed against the capstan 8 by the normal pressure T. Consequently, the magnetic tape 6 may possibly slip relative to the capstan 8, and the pinch roller 1 needs to be replaced with a new one when such a permanent depression is formed in the rubber coat 1a.
The upper and lower end portions 1c of the pinch roller 1 coated with the rubber coat 1a are in contact with the capstan 8 in comparatively large widths of contact area W.sub.1 and W.sub.1 ', which are dependent on the pressure T and the hardness of a rubber material forming the rubber coat 1a, so that the pinch roller 1 is rotated by the capstan 8 to drive the magnetic tape 6 together with the capstan 8. Accordingly, if the pinch roller 1 and the capstan 8 are misaligned, the widths of contact area W.sub.1 and W.sub.1 ' of the upper and lower end portions 1c of the pinch roller 1 are greatly different from each other, and there by the magnetic tape 6 will be caused to run in a direction T.sub.L or T.sub.R (FIG. 8) deviating from the normal running direction T.sub.0, so that the edges of the magnetic tape 6 are damaged by tape guides.